﻿5HE CATTLE GRUBS OR OX WARBLES 71 



Iwliile the fly remains on the ground. When the animal moves, the 

 fly usually follo^Ys, flying behind close to the ground, and when the 

 opportunity offers she may alight on the host, commonly on the 

 hind legs below the hock. Under such conditions the animal is 

 usually aware of the presence of the fl}^ and often kicks at it, fre- 

 ([uently loiocking it to the ground, in which case it usually arises 

 promptly and starts again after the host. With animals disturbed 

 in this wa}^ the ^j is more likely to attack higher on the legs and 

 not infrequently on the sides, especially in the region of the flank 

 or on the forelegs or shoulders. 



In many instances the writers have observed females of H. Unea- 

 tiim to oviposit on cattle while they were lying down. When not 

 disturbed the fly usually deposits a series of eggs, possibly 50 to 

 60, in rapid succession and then rests for a minute or two. Some- 

 times she moves slightly to a new position and then repeats the 

 operation. 



Flies of H. Uneatum captured by means of a net while attacking 

 cattle in nature are readily induced to oviposit on experimental 

 animals kept under control; in fact., this was the method followed 

 in obtaining eggs with which to infest experimental animals and 

 for other purposes. After the flies were captured they were usually 

 placed in small tubes or jars and brought immediately to the 

 laboratory and placed upon experimental hosts. To' accomplish this 

 the female was usually placed in a glass.' vial with the open end 

 placed against tlie host. Usually as soon as the fly comes in con- 

 tact with the hair of the animal she begins extending the ovipositor 

 and starts laying eggs. After she has once begun it is often unneces- 

 sary to keep the restraining vial over her. 



H. hovis attacks the animals; viciously, usually approaching them 

 about the height of the hock, and very seldom lights on the ground. 

 On account of its more persistent and ferocious attack the animals 

 are put to flight with the first period of oviposition. The fly strikes 

 the animal a number of times in rapid succession, cementing an 

 egg on a hair in nearly every instance. After a number of these 

 strikes at the animal the fly may leave for a. few minutes and then 

 return and repeat the process as persistently as before. Frequently 

 when tlie host is active the fly may follow it around a small pas- 

 ture, attacking repeatedly when it catches up to the fleeing animal. 



Great difficulty was experienced in getting females of H. hovis 

 to deposit eggs after tliey had l)een captured. Hawclen's reports 

 indicate that he had no difficulty in getting females caught while 

 ovipositing in natui-e to. deposit under an insect net held to a bovine 

 or when released near a tethered animal. In Illinois and New 

 York, liowever, a number of flies ca|)tured in the field by the writers 

 and applied in various ways to hosts under control gave very dis- 

 couraging results. Only a few eggs were secured and these for the 

 most part were dropped free in the hair. 



During the summer of 1922 a large number of flies of both sexes 

 of //. hovi<^ were reared at Middletown, N. Y., and many attempts 

 were made to secure eggs from tliom. Although they mated freely, 

 as has l>een stated, they persistently refused to oviposit. Some wei'e 

 kept in glass containers lidd against a calf; others were i)laced in 

 small screen cages attached to the host; and still others were liberated 



